I have a developement board and I have found the schematic of it. However, When I skim through schematic, I came across this charger and boost circut but I couldnt figure out what is the purpose of N channel MOSFET (NCE3401AY) that connected to li-po connector. Any guess is appreciated.
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That's not an N-channel MOSFET, it's a P-channel one.
The application here is classic reverse polarity protection; if the battery is connected backwards, the FET will be turned off (protecting the rest of the circuit from damage from the negative voltage), but if connected correctly it will turn on.
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\$\begingroup\$ why they didnt use a single diode? is it because voltage drop of diode? \$\endgroup\$– enisCommented Sep 16, 2023 at 16:52
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2\$\begingroup\$ @enis Yes, a diode has a voltage drop, but a FET in the on state has much less of one, especially if you choose a very low-Rdson device. The drop of a Schottky diode would be about 0.3 V, while the drop of this FET would be something in the range of 50 to 100 mV per amp of current (depending on the battery voltage). \$\endgroup\$– HearthCommented Sep 16, 2023 at 16:54